The immunological responses to unmethylated CpG motifs on plasmid DNA (Tan et al., 1999, Hum. Gene Ther. 10:2153-2161), cationic lipid formulations (Tousignant et al., 2000, Hum. Gene Ther. 11:2493-2513), and lipid/DNA lipoplexes (Tousignant et al., 2000, Hum. Gene Ther. 11:2493-2513; Scheule et al., 1997, Hum. Gene Ther. 8:689-7071; Li et al., 1999, Am. J. Physiol. 276:L796-L804) present major obstacles to nonviral gene delivery. Although transgene expression occurs within hours after plasmid delivery (Li et al. 1999, Am. J. Physiol. 276:L796-L804) the immunostimulatory cytokines TNF-α and IL-6 are also detected by one hour after systemic (Tousignant et al. 2000. Hum. Gene Ther. 11:2493-2513) or intranasal (Scheule et al. 1997, Hum. Gene Ther. 8:689-7071) administration. Other immunomodulatory cytokines, such as IFN-γ and IL-12, remain elevated for several days thereafter (Lasic, 1997, Liposomes in Gene Delivery, CRC Press). This rapid immune response to lipoplexes resembles the acute phase response to infection, which consists of local tissue reactions and systemic reactions by the liver, mediated chiefly by the inflammatory cytokine IL-6 (Streetz et al, 2001, Cell. Mol. Biol. 47:661-673). The inflammatory cytokines lead to an activation of endothelial cells and an influx of neutrophils, lymphocytes, and macrophages at the site of gene delivery (Tousignant et al. 2000, Hum. Gene Ther. 11:2493-2513; Scheule et al. 1997, Hum. Gene Ther. 8:689-7071). As a result, immunological responses to nonviral DNA delivery decrease the magnitude and duration of expression of the transgene and decrease the effectiveness of frequent dosing (Li et al. 1999, Am. J. Physiol. 276:L796-L804). Pharmacological doses of anti-inflammatory glucocorticoids prior or concurrent to administration of lipoplexes have a positive impact on inhibiting an immune response to a plasmid, resulting in an increased amount and duration of transgene expression, increased lifetime of plasmid, and shortened windows of time between dosing (Tan et al. 1999. Hum. Gene Ther. 10:2153-2161; Braun et al., 1999, FEBS Letters 454:277-282; Wiseman et al., 2001, Gene Ther. 8:1562-1571).
Glucocorticoids bind the glucocorticoid receptor (GR), inducing exposure of a classical nuclear localization sequence that allows importin α/β1 binding and subsequent trafficking into the nucleus (Galigniana et al., 1999, J. Biol. Chem. 274:16222-16227; Savory et al., 1999, Mol. Cell. Biol. 1025-1037). Glucocorticoids are also potent anti-inflammatory molecules that regulate the immune system by: (1) inhibiting the production or release of major cytokines such as IL-1, IL-6, TNF-α and IFN-γ; (2) decreasing the stability of mRNA encoding IL-1, IL-2, IL-6, IL-8, TNF-α, and GM-CSF; and (3) inhibiting cytokine-induced transcription by AP1 and NF-κB via the GR (Ashwell et al., 2000, Ann. Rev. Immunol. 18:209-345; McEwan et al., 1997, Bioessays 19:153-160; Schimmer et al., 1996, in The Pharmacological Basis of Therapeutics 1459-1485, McGraw-Hill). Liganded GR forms dimers that bind 15 base-pair glucocorticoid response elements (GREs) to induce or repress transcription (Schimmer et al., 1996, in The Pharmacological Basis of Therapeutics 1459-1485, McGraw-Hill; McNally et al., 2000, Science 287:1262-1265).
Viral and non-viral vectors are used as the basis for gene delivery in current nucleic acid and gene therapy methods. However, there are concerns about the production, reproducibility, cost, and safety of viral vectors for gene therapy. As a result, work has focused on the development of nonviral vectors where the gene construct of interest is packaged by synthetic nonviral materials. Examples of such materials include polycations, dendrimers, and polysaccharides, as well as small molecule cationic lipids such as dioleylphosphatidylethanolamine (DOPE), 3-beta-[N′,N′ dimethylaminoethane)-carbamoyl]cholesterol (DC-chol), and spermine cholesterol. For example, cationic lipids for lipofection condense plasmids, facilitate endosome escape, neutralize charge of DNA, and/or shield DNA from nucleases (Lasic, 1997, Liposomes in Gene Delivery, CRC Press).
There is a long felt need in the art for the development of new compositions and methods for nucleic acid delivery which produce high levels of transfection and for drug delivery which produce high levels of incorporation into a cell, and which also includes the ability to deliver drugs locally. There is also a need for such a delivery platform which has inherent pharmacological or biological activity and increased pharmacokinetic half-life and sustained depot action. The present invention satisfies these needs.